Phase level system

ABSTRACT

System to determine the height in liquid or molten metal levels or phases within a mat or slag converter or pyrometallurgical furnace, whereby it comprises a signal generator and a signal processor, where such generator sends an electrical signal to such processor, being such processor connected to a group of electrodes placed in the converter&#39;s shell or pyrometallurgical furnace, in which such electrodes are disposed crossing the shell in electrical contact with the phases so that they are installed in height zones of the slag and metal levels or phases, so that once such electrodes are installed configuring serial resistance groups through which such electrical signals circulate.

The following invention is directed towards a method and system todetermine the level height of liquid or molted metals inside metal, mator slag converters or furnaces. It is specifically directed towards amethod and system that by the application of a sign external to themelting bath is possible to determine the height of phases on line,being able to obtain the height from the slog-mat interface and thetotal level of the bath.

PREVIOUS ART

In pyrometallurgical converters or furnaces, basically three immiscibleproducts coexist, composition and different physicochemical properties;Gas, Mat (high grade phase) and slag (low grade phase). These areseparated by phases, thus presenting a Gas-Slag interface and anotherSlag-Mat interface which height with respect to the converter orfurnace's bottom is denominated total level and mat level, respectively.

Currently, it is particularly difficult to estimate those levels with anacceptable precision during pyrometallurgical processes. However, theseconstitute fundamental parameters regarding decision making ofoperations and metallurgical accounting. In effect, the inadequatecontrol of the phase's levels, resulting from a poor measurement, willalways result in fewer metal recoveries due to losses of mat or slag, orelse, insufficient consumption of energy in the operation. This makesmonitoring and control of the total level and mat level an essentialtool to obtain an optimum operation and thus reduce losses.

In the previous art, different useful technologies are known for themeasurement of levels within converters or furnaces.

Currently, the most widely used method consists in estimating the phaselevels starting from visual inspections of steel rods at carbon-20, ofgreater length than the converter or furnace's diameter, periodicallysubmerged in the metallurgical bath vertically through an opening in theconverter or furnace's upper part and removed after a time of residenceof a few minutes in the metallurgical bath. A strong chemicaldeterioration can thus be observed in these rods in the zone exposed tothe mat phase, which permits to estimate the mat level and slag adhesionup to the height corresponding to the maximum level.

This method is fairly simple in its implementation, but conveys a riskto the operator. Likewise, the sampling precision and frequency thatthis method offers is low, therefore the timely and precise knowledge ofeach phase during operation continues to be a problem without solutionor only a partial solution in the pyrometallurgical processes.

Another method used in the previous art corresponds to a densimeter orFloating Buoy. By having each liquid a different density within theinside of the converter or furnace, it is feasible to think of a methodthat detects the heights upon which they vary, and thus, know each ofthe existent phase changes. Its operation would be greatly similar tothe use of a spear, considering the introduction of the instrument inthe converter or furnace supported by a spear that serves as a heightmeasuring tool of the respective level heights.

The high temperatures existent in the interior of the converter orfurnace force for the use of a densimeter capable of resisting operationtemperatures greater than 1250° C. (2282° F.), to which the liquids tobe measured are subject to. Without a doubt, this inconvenience hamperseven more the operation and the life of the instrument to be utilized.

The inconveniences that the previous art methods present lie, firstly,in their poor precision, given that the metallurgical bath is inconstant movement producing widespread marks over the rods which arehard to accurately interpret, therefore the estimation so obtainedrepresents only another threshold for the continuance of the conversionprocess in the converter or furnace. Secondly, the relative frequencythat such measurements may be carried out, diminish the timelyinformation inferred from them.

Additionally, the previous art has also described a system of discreetand continuos measurement of levels, based on the application ofmechanical waves (ultrasonic). For example, the following patentpublications can be mentioned:

Rojas et al: “System for a non-invasive online discrete measurement ofphase level in converters or pyrometallurgical furnaces”. U.S. Pat. No.6,836,734 B2, Dec. 28, 2004

Rojas et al: “System for a non-invasive online continuos measurement ofphase levels in converters or pyrometallurgical furnaces”. U.S. Pat. No.6,792,358 B2, Dec. 28, 2004

Additionally, the previous art has also described a discrete andcontinuos measurement of levels, based on electro-resistant principles.For example, the following patent publications can be mentioned:

Woodcock, Ray E. et al. “Hot metal level detector”. U.S. Pat. No.3,395,908, Aug. 6, 1968

Tenberg et al. “Device for measuring the level of the interface betweena slag layer and the bath of molten metal in a metallurgical vessel”.U.S. Pat. No. 4,554,140, Oct. 1, 1985.

Both publications mention the development of detectors able to performcontinuos measurements of phase levels, based on spear type assembly.However, this type of system does not allow to carry out onlinemeasurements.

Notwithstanding the above, the previous art nearest this invention, isrepresented in the publication by Usher John D. “Refractory materialsensor for determining level of molten metal and slag and method using”.U.S. Pat. No. 6,309,442, since it is mentioned in this patentpublication the disposition of electrodes at different heights in whichthe proposed device contemplates piercing the refractory withelectrodes, in this case wire conductors (not solid electrodes as inthis application) which at the beginning does not necessarily come intocontact with the metallurgical bath. Notwithstanding, the operationalprinciple of the sensor is based on the Seebeck effect (commonlyutilized in thermocouples) and the “Double layer” effect which is thepropeller electromotive force (EMF) between the volume of an ionic phaseconduction such as slag and the layer which is produced in the interfacewith an electronic conduction material such as metal. This principle, isfar from the electro-resistant principle applied in this application,since in the mentioned publication small potentials are measured whichare generated by putting into contact two materials of differentelectronic nature. On the other hand, in this application, theelectronic response in a metallurgical bath is studied at a controlledand external electronic stimulation.

It must also be considered that the Usher system does not deliver acontinuos level measurement, but rather a discrete measurement,therefore the level measurements corresponds to a discrete level.

In this sense, the basic advantage of the current application, discreteas well as continuos measurement, with respect to the systems developedby Woodcock and Tenberg is the possibility to be implemented online.Further to the already mentioned surface exposed to chemical corrosionwhich in the present invention is much less.

Moreover, the advantage of the proposed invention compared to the Ushersystem and method, is based on the ability to measure the levels in awide range, along the converters or furnaces and not in a specificmanner to a certain specific height of the container, which only servesto identify when the slag-mat interface passes along that specificheight or, at the most in a discrete manner, thus needing a great amountof probes (or electrodes) to reach an acceptable height resolution. Buteven more importantly, the system and method herein proposed allows tovary, in a wide range, the intensity of the stimulating signal and thusthe amplitude of the responses. This capacity is crucial in theacquisition of signals in industrial environments, where the high levelof noise may widely exceed the amplitudes of smaller signals comprisedin the chemical interactions proposed by Usher.

BRIEF DESCRIPTION OF THE FIGURES

FIG. 1: represents a scheme which illustrates the operation of theinvention system with sensors measuring the phase levels.

FIGS. 2 a and 2 b: represent a scheme which illustrates the measuringsystem composed by a stimulating branch, another branch of acquisitionand a sequence device that coordinates both branches.

FIG. 3: represents a scheme of the resistance measuring mechanism. (a)corresponds to the scheme of a pair of electrodes submerged in one ofthe metallurgical bath phases with the purpose of exemplifying themethod of the invention. (b) Corresponds to a circuit equivalent to apair of submerged electrodes whereby the way in which the measuring isperformed in such invention method is illustrated.

FIG. 4: represents a scheme of electrode configurations for discretemeasuring, specifically in an option of co-lineal electrodes.

FIG. 5: represents a scheme of electrode configurations for discretemeasuring, specifically in a configuration option of co-linealelectrodes.

FIG. 6 a: represents a scheme which illustrates a configuration toperform the discrete estimation method.

FIG. 6 b: represents a circuit equivalent to the configuration of amethod of discrete estimation.

FIG. 7 a: represents a scheme which illustrates a configuration toperform the continuos estimation method.

FIG. 7 b: represents a circuit equivalent for the configuration of acontinuos estimation method.

DETAILED DESCRIPTION OF THE EMBODIMENTS

The method of the invention is based on the measurement of electricalresistance through the phases present within a pyrometallurgicalconverter or furnace. To this effect, it is known that measurements ofspecific electrical conductance (opposite to the resistivities), showdifferences of various nature of magnitude, between mat and slag, forexample, for white metal and slag, the studies carried out by Pound, G.M., Degre, G. and Osuch, G. (1955) “Electrical conduction in moltenCu—Fe sulphide mattes”. Trans A.I.M.E. 203, 481-484, show values of 300to 1000 Ω⁻¹ cm⁻¹ in white metal and 0.5 Ω⁻¹ cm⁻¹ in slag. Similarresults were obtained by Otero, A. and Garcia, M. (1992) “Study ofheight level measurement of molten phases in copper concentratedconverter furnaces”. CIMM, Extractive Metallurgical Division, P-833, inwhich studies of electric properties of molten phases coexistent in theinterior of copper concentrated converter furnaces, upon which themethod of invention proves that it is possible to take advantage ofthese electrical differences in said phase, for the construction of amethod and system capable of measuring the total level of themetallurgical bath as well as the slag-white metal interface.

The method consists in performing sequenced measurements of potentialfalling between electrodes (1) immersed at certain heights of the bathrepresented by phases (3) (4) and (5), as illustrated in FIG. 1. Togenerate these measurements, a system composed of two branches isprepared; stimulating branch and acquisition branch, duly synchronizedthrough a sequence device (8), showed in FIG. 2.

The stimulating branch is made up of an current source (6), of variableintensity I₀. The electricity so generated is modulated by a sequencedevice (8) of adjustable synchronization which alternately andsequentially closes the contacts between the current source (6) andelectrodes (1) for adjustable and relatively short periods of time τ,during which an electrode (9) will be the transmitter, sending a pulseof electricity of I₀ intensity through the phase in which it is immersedand which shall be received by the other electrode (10), closing thecircuit.

Furthermore, the acquisition branch, made up of a voltmeter (7), whichmeasures during time τ, the potential difference between thetransmitting electrode (9) and the receptor (10), assigned by the samesequence device, which closes the contact between the receptor electrode(10) and Voltmeter (7).

Starting from these measurements, the electric resistance (R_(m)=V/I₀),that some regions between electrodes (9) and (10) offer may then beinferred, such regions being composed by phases.

The electric behavior of the system composed by a pair of electrodes (9)and (10) submerged in a specific phase of the metallurgical bath, asillustrated in FIG. 3 a, in which said electrodes an I₀ current is madeto circulate, can be described as a serial resistance group, just as itis shown in FIG. 3 b.

The resistance of phase (R_(f) in FIG. 3 b) can always be expressed interms of the specific electric resistivity of the phase and geometricalparameters of the electrodes and their availability. However, whicheverthe geometry and separation of the electrodes, this resistance willalways be directly proportional to the specific electric resistivitywhich characterizes the phase between the electrodes. Therefore, themeasured resistance R_(m), is a product of the resistive contributionsof the electrodes and wiring plus the phase's resistance, this is:R _(m) =R _(em)+R_(re)+2R _(c) +R _(F)With, R_(F)=ρ·G(r, d, a)Where,

-   -   R_(em) and R_(re) represent the resistance of the transmitting        and receptor electrode, respectively.    -   R_(c) represents the wiring resistance of an electrode    -   R_(F) represents the phase's resistance    -   G(r, d, a) corresponds to an independent function of the        geometry and disposition of the electrodes.

Therefore, the resistances so measured will be much higher formeasurements executed in slag than for those executed in white metal andpractically infinite for measurements performed in gas. This way, inconjunction with the fact that the height of the electrodes is known,real time information will be achieved with respect to the levels of thephases in the interior of converters or furnaces.

The system of the invention contemplates two preferred embodiments ofexecution. The first preferred embodiment contemplates a continuos andon line determination system of phase levels and the second embodimentcontemplates a discrete and online determination system of such levels.Both embodiments are based on the above mentioned method, differingamongst them only by the arrangement of immersed electrodes in thephases and interpretation criteria of the signals, as explained below.

In the case of the discrete determination embodiment, the systemcontemplates electrodes densely disposed around historic height zones oftotal and mat level which is known by experience, for example, of thespear introduced in the previous art as shown in FIG. 4 where pairs ofelectrodes are placed in a collinear manner. Such manner is not strictlynecessary, being able to place the electrodes even in zigzag, as shownin FIG. 5, so long as the height in which they are placed is known. Thisway, if a pair of electrodes immersed in the gaseous phase isconsidered, another in the slag phase and another in the mat phase, asshown in FIG. 6, so long as the sequence device activates the readingbetween the electrode pairs, it will be observed that R_(m12)>>R_(m34)and R_(m34)>>R_(m56), from which it can be inferred that between theheight of electrodes E2 and E3 the Gas-Slag interface is found andbetween the height of electrodes E4 and E5 the Slag-Mat interface can befound. Thus, the levels can be estimated upon the sudden variationsobserved and the measured resistances and the heights known byconstruction of the electrodes, in which these variations may beobserved, with an uncertainty given by half of the separation betweenthese electrodes, without determining the exact height in which thephases may be found, therefore the levels are determined only discretelyby knowing that the interface is found between two particularelectrodes, but not at which height. In this manner, the density of theelectrodes around the historic heights of the slag-mat levels, willdepend of the discrete resolution wished to be obtained.

In the continuos determination embodiment, the dense disposition ofelectrodes is not required, since the criteria of level estimation iscapable of determining the interface height between two particularelectrodes.

For the case of Total Level, the estimation criteria supposes theexistence of an accretion layer in the wall of the converter or furnacethrough which the electrodes are installed. These electrodes shall bedisposed in such a way that at least one electrode is at all timesimmersed in each phase, as shown in FIG. 7 a. In this way, the electricbehavior of this system can be modeled as the resistance configurationsillustrated in FIG. 7 b.

Without further elaboration, it is believed that one skilled in the artcan, using the preceding description, utilize the present invention toits fullest extent. The preceding preferred specific embodiments are,therefore, to be construed as merely illustrative, and not limitative ofthe remainder of the disclosure in any way whatsoever.

In the foregoing and in the examples, all temperatures are set forthuncorrected in degrees Celsius and, all parts and percentages are byweight, unless otherwise indicated.

The entire disclosure[s] of all applications, patents and publications,cited herein are incorporated by reference herein.

The preceding examples can be repeated with similar success bysubstituting the generically or specifically described reactants and/oroperating conditions of this invention for those used in the precedingexamples.

From the foregoing description, one skilled in the art can easilyascertain the essential characteristics of this invention and, withoutdeparting from the spirit and scope thereof, can make various changesand modifications of the invention to adapt it to various usages andconditions.

1. System to determine the height in liquid or molten metal levels orphases within a mat or slag converter or pyrometallurgical furnace,whereby it comprises a signal generator and a signal processor, wheresuch generator sends an electrical signal to such processor, being suchprocessor connected to a group of electrodes placed in the converter'sshell or pyrometallurgical furnace, in which such electrodes aredisposed crossing the shell in electrical contact with the phases sothat they are installed in height zones of the slag and metal levels orphases, so that once such electrodes are installed configuring serialresistance groups through which such electrical signals circulate. 2.System to determine the height of phases according to claim 1, whereby aset of electrodes is installed above a certain phase level and anotherset of electrodes is installed under such phase level.
 3. System todetermine the height of phases according to claim 2, whereby, eachelectrode set is composed by at least two electrodes in case thedetermination of phase heights is discrete.
 4. System to determine theheight of phases according to claim 2, whereby, each electrode set iscomposed by at least one electrode in case the determination of phaseheights is continuous.
 5. System to determine the height of phasesaccording to claim 2, whereby in a preferred embodiment, such electrodesare installed in a collinear manner.
 6. System to determine the heightof phases according to claim 2, whereby in a preferred embodiment suchelectrodes are installed in zigzag.
 7. System to determine the height ofphases according to claim 1, whereby such electric signal is an electriccurrent which circulates through such electric circuit.
 8. Method todetermine the height of liquid or molten metal within metal, mat or slagconverters or pyrometallurgical furnaces whereby the method consists inmeasuring the electric resistance of such liquid metal and/or slagphases present in such converter or pyrometallurgical furnace, so thatthrough the differences in such electric resistances detected in eachphase the height in which each one of the is places is determined; inthat such measurement consists in determining the potential fall betweena group of electrodes placed at different heights in the shell of suchconverter or furnace, being such electrodes submerged in contact in suchphases, and conforming a serial group of resistance, by which throughsuch electrodes a circular current is made to circulate, such currentcoming from a signal generator system and modulated by a signalprocessor, so that once such current circulates, the electricresistances of the regions comprised between such electrodes areinferred, so as to obtain a real time measurement of the height levelsof such phases inside said converter or furnace.
 9. Method to determinethe height of phases according to claim 8 whereby the resistance of eachphase is directly proportional to the specific electric resistivity thatcharacterizes each phase between electrodes.
 10. Method to determine theheight of phases according to claim 9 whereby the measured resistance isobtained by the electrode resistance plus the wire resistance, throughwhich such resistances are connected, plus the resistance phase.